The present invention relates to a water softener for reducing water hardness, suitable for use in a household washing machine, in particularly a dishwasher, and to a control method for checking the degree of exhaustion of the water hardness reducing substance.
It is well-known that household washing machines operating with water, more particularly dishwashers, can be equipped with a device for decalcifying the washing and rinsing water, i.e. for reducing the degree of water hardness, so as to avoid otherwise likely calcareous scale deposits. Such a device is also known as a water softener. Calcareous scale deposits are caused by an extremely high quantity of calcium ions (Ca++) and magnesium ions (Mg++) contained in the washing water. Such a decalcifier exchanges both the calcium ions (Ca++) and magnesium ions (Mg++) contained in the water for sodium ions (Na+) contained in appropriate resins placed in the decalcifier.
Resins or other similar substances, herein called resins for simplicity""s sake, become exhausted after a certain time of usage, i.e. their Na+ ions to be exchanged with Ca++ and Mg++ contained in the water are consumed. As a result, water will still flow through resins but substantially maintain its starting hardness. The higher the water hardness is, the faster the resins will become exhausted.
This drawback is prevented through a phase where resins are regenerated by introducing a water-salt solution (NaCl). This resins regeneration phase is generally executed for each wash cycle, thereby requiring that a considerable quantity of salt be used, and often requiring that it be introduced by the user. Moreover, greater water consumption also results.
It is well-known that with a view to reducing salt and water waste some washing machines are equipped with water hardness sensors by which resins regeneration is activated only when water hardness is not sufficiently reduced due to resins exhaustion. The sensors are used to measure the water resistivity and, from the results obtained through an electronic system, the resins regeneration will either be activated or not.
The foregoing system requires that electrodes be dipped in the water and electrically energized. Although a low voltage is applied to the sensors, there will always be a danger, because these sensors are in direct contact with water. Moreover, even if water hardness is reduced, nothing prevents a light calcareous layer from being deposited on the sensors before resins regeneration is activated, thus altering water hardness detection due to the additional calcareous resistivity. Such systems detect water hardness directly, whereas resin status is detected only indirectly. As a result, resins regeneration will sometimes be activated in instances where it is not yet required.
An object of the present invention is to overcome the aforementioned drawbacks and provide, in particular, a device for reducing water hardness, i.e., a softener, which is suitable for use in a household washing machine, in particular a dishwasher, wherein detection of exhaustion of the reducing substance is realized in a simple, safe, inexpensive and direct manner.
Within this framework, it is an object of the present invention to provide a device for reducing water hardness, i.e., a softener, which is suitable for use in a household washing machine, in particular a dishwasher, a control method to check the degree of exhaustion of the water hardness reducing substance, and a washing machine using such a device, all having the features of the annexed claims which form an integral part of the present description.
Further aims and advantages of the present invention will become apparent from the following detailed description and the annexed drawings, which are supplied by way of non limiting example, wherein: